(1) Field of the Invention
This invention relates to the use of masks using attenuating phase shifting material for regions of the pattern with relatively large spaces between lines and binary mask patterns using opaque material for regions of the pattern with relatively small spaces between lines on the same mask substrate. The mask is illuminated using off axis illumination when using the mask to form a pattern on an integrated circuit wafer. The mask is formed using a single resist layer exposed using multiple electron beam exposure doses.
(2) Description of the Related Art
U.S. Pat. No. 5,481,332 to Shiraishi describes a projection exposure method and apparatus for improved image transfer from photomasks having periodic and non-periodic patterns. The projection optical system uses off axis illumination to illuminate the photomask.
U.S. Pat. No. 5,503,951 to Flanders et al. describes a method of forming a photomask using attenuating phase shifting material.
U.S. Pat. No. 5,480,747 to Vasudev describes a method of forming a photomask using attenuating phase shifting material and using embedded absorbers.
A Patent Application (TSMC-97-201) entitled "A NEW DOUBLE LAYER METHOD FOR FABRICATING A RIM TYPE ATTENUATING PHASE SHIFTING MASK", Ser. No. 08/956,971, Filed on Oct. 3, 1997, and assigned to the same assignee describes a method of forming multiple patterns in a single layer of resist using two different electron beam exposure doses.
A Patent Application (TSMC-97-261) entitled "A MASK AND SIMPLIFIED METHOD OF FORMING A MASK INTEGRATING ATTENUATING PHASE SHIFTING MASK PATTERNS AND BINARY MASK PATTERNS ON THE SAME MASK SUBSTRATE", Ser. No. 09/020,502, Filed on Feb. 9, 1998, and assigned to the same assignee describes a binary mask pattern and a rim type attenuating phase shifting mask pattern formed on the same transparent mask substrate.
A paper entitled "Optimization of the optical phase shift in attenuated PSM and application to quarter micron deep-UV lithography for logics" by K. Ronse et al., SPIE Vol. 2197, pages 86-98 discusses optical techniques to achieve optimization of attenuated phase shifting masks.
A paper entitled "Quarter Micron Lithography System with Oblique Illumination and Pupil Filter" by S. Orii et al., SPIE Vol. 2197, pages 854-868 discusses the usefullness of pupil filtering.
A paper entitled "Dependency of side-lobe effect of half-tone phase shift mask on substrate material and topology, and its solutions" by Sung-Chul Lim et al., SPIE Vol. 2512, pages 372-383 discusses loss of resist due to side lobe effect.